Google recently announced new policies regarding the use of their APIs and third party integrators (such as pdfconvert.me). You can review the announcement here.
One of the requirements to continue the use of the restricted scopes (of which the service uses 3: gmail.readonly, gmail.modify (to modify the Pre/Post Labels only) and gmail.send), a third party security assessment is required, which can cost $15,000 USD or more.
While I understand why Gmail is requiring the new policies and assessments, and while I regularly undergo these sorts of security assessments as part of my regular day job, for the limited number of users on a free service, this is not something I am willing to pay for in either time or money.
As such, consider this an end of life announcement for the Gmail API integrations with pdfconvert.me. You can still use the service with Gmail by setting up automatic forwarding rules to the @pdfconvert.me addresses, but the API integrations will cease to function in the future when Google terminates my application’s approval.
I am disabling new signups to the service as of today (November 11th, 2018) but will continue to operate on existing accounts as long as Google (or you) allow. As a reminder, you can always revoke access to pdfconvert.me via your Google account or I am happy to delete your account on my end (please email email@example.com).
Please let me know if you have any questions, and thank you for your support.